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Narrator: Our story begins in the deep, dark universe, where galaxies, like people, lead fascinating lives, filled with drama.

Thaller: Galaxies are born, they go through a very troubled childhood, they kind of blow up, they get very unstable in their teen years, and then gradually they settle down, they become mature adults, ready to assume their place in the galactic culture. But even when they're adults, there are all kinds of things that can happen. There can be mergers, they can rip each other apart. There can be marriages they can come together and form a single galaxy.

Narrator: Dr. Michelle Thaller, outreach scientist with NASA's infrared Spitzer Space Telescope, will guide us through the life of a galaxy, along with others from Spitzer and another NASA observatory, Galaxy Evolution Explorer.
But first, back to this galactic marriage thing.

Thaller:
A lot of times you see two galaxies come careening towards each other. And you can basically say that as these two are attracted to each other, you're either headed for a marriage or a divorce because sometimes the galaxies will glom together and form one big galaxy. Hey, let's hope for a happy married life there. Sometimes they rip each other apart. Just tragic, heartbroken. And they also grow old, too. Galaxies go through stages in their life where there's lot of active star formation, there's lots going on, life is very exciting, and then, well, things calm down. Eventually there aren't so many stars being formed, eventually the stars themselves begin to grow old and, well, you're in for a quiet middle age.

Narrator: Spitzer and Galaxy Evolution Explorer, or Galex, study the life stages of galaxies. Because Spitzer looks for infrared heat, and Galex looks for ultraviolet light, they detect different things. Dr. Chris Martin of Caltech is principal investigator for Galex, which is studying galaxies - the early years.

Martin: It's very difficult to observe galaxies early in the process of formation. We can see them early in their history, but they're so far away that we get very little information about them. With Galex, for the first time, we've discovered galaxies that look like forming galaxies from the early universe. And now, but these galaxies in our own backyard, they're very rare, but we have enough of them, we can start studying what a galaxy looks like when it's born.

Narrator: OK, so as Michelle said, eventually baby galaxies become toddlers - in their terrible twos. Or two billions - two billion years, that is or more. The Spitzer Space Telescope watches from afar. Project Scientist Dr. Michael Werner of JPL.

Werner: The Large Magellanic cloud, which is a nearby satellite of the Milky Way, of our Milky Way galaxy, it's a galaxy which may someday be swallowed up and engulfed by our galaxy. It's probably a good example of a toddler, and it's a very nearby toddler and so we can get a very, very good look at it. And you can see it's kind of unruly like a toddler, its going this way and that. And we have beautiful images now showing the full range of structures and processes going on in that galaxy.

Narrator: So after a tumultuous childhood and teenage years, each galaxy enters the cosmic meat market, interacts with other galaxies, and might even get married.

Werner: We've obtained a number of exciting images of interacting galaxies which show in stark resolution or with high contrast, the regions where the interaction is triggering the star formation process.

Narrator: Then it's time to settle down for an era of galactic contentment.

Werner: My favorite Spitzer image of a galaxy is actually our composite of M81, which we made early on in the mission. M81 is what you might call an adult galaxy, it's a good neighbor, it's a member of its Rotary Club, it's not doing anything too extravagant. And when we look at the Spitzer image, we can see sort of spread out on the sky, and M81 is a very big galaxy, the various components that make up a galaxy, we can see a dense stellar bulge at the center, we can see the material in the spiral arms of the galaxy, and we can see clustered in the spiral arms, regions of star formation which stand out sort of like Christmas tree bulbs.

Narrator: Then there's the galactic aging process.

Werner: As we look in the nearby universe, we see two types of galaxies: spiral galaxies, which are rich in dust and gas, and so-called elliptical galaxies, which mainly contain stars. The elliptical galaxy ages gracefully, rides off into the sunset, and as it does this, we can continue to study it with Spitzer, because as its stars cool and age, their radiation again emerges in the infrared spectrum that Spitzer is sensitive to. The type of star-forming activity that Galex is sensitive to is less prevalent in these galaxies, because their fuel, their dust and gas, they've eaten all their food, if you like.

Narrator: And the final act for a galaxy?

Thaller: We don't know how galaxies will eventually die, because we're still wrapped up in that process right now. And we can't exactly see into the future.

Narrator: So what is our role in this galactic soap opera? Chris Martin.

Martin: There are sort of several major questions. First of all, the universe started out uniform, full of matter, but all uniform. How did structure form, how did galaxies form, and clusters of galaxies? And you see this beautiful cosmic web, where galaxies are lined up everywhere. So we would like to understand that because ultimately, we were born around a star and we'd like to understand how we got here, how our galaxy got here, how our star got here.

Narrator: Thanks to Chris Martin, Michelle Thaller, and Michael Werner for starring in this galactic soap opera. More info on the Spitzer Space Telescope is at www.spitzer.caltech.edu . On Galaxy Evolution Explorer at www.galex.caltech.edu .
Thanks for joining us for this podcast from NASA's Jet Propulsion Laboratory.